The present invention relates to mitigating crack initiation or growth of small cracks in a nuclear reactor vessel and, more particularly, to an implementation/scheduling process for mechanical surface conditioning of metals to mitigate crack initiation or growth. Delivery of other processes to the component surfaces is also contemplated.
The welds in the bottom head region of a reactor vessel in a boiling water nuclear reactor are susceptible to cracking. Repair of such cracking requires complex and expensive processes. A known ‘ReNew™ process’ has been used to mitigate susceptibility to crack initiation or growth of small cracks due to tensile surface stresses, stress corrosion initiation and fatigue crack initiation using a mechanical surface conditioning of metals. These stresses can be found in the welds and heat affected zones of the reactor bottom head. The quantity of welds in the vessel head region, however, is very large, and it is typically very time consuming to mitigate all welds.
To the inventors' knowledge, mitigation of all bottom head welds in a reactor vessel has never been done. Prior methods have performed mitigation using water jet peening or laser shock peening.
For those reactors going through a shroud replacement process, bottom head weld mitigation is economically viable if mitigation can be performed in about thirty days or less. It would thus be desirable to provide a renew process implementation/scheduling process to mitigate all bottom head welds in a reactor vessel in an economically viable period of time.